Flat gasket, in particular for an internal combustion engine and related manufacturing method

ABSTRACT

A sheet gasket, particularly for internal combustion engines, consisting of at least one metal sheet forming a core which is cut to match the mating face, and elastomeric portions, particularly in bead form, which are bonded to the sheet around holes to be sealed. The gasket includes a single-piece elastomeric covering placed on part of the sheet surface to form localized sealing projections around the holes to be sealed. A related manufacturing method is also provided.

This application is a continuation of U.S. patent application Ser. No.08/204,408, filed May 5, 1994 now abandoned.

FIELD OF THE INVENTION

The present invention relates to a flat gasket, in particular for aninternal combustion engine, and to the related manufacturing method.

BACKGROUND OF THE INVENTION

Flat gaskets, in particular for a sump employed in internal combustionengines, must be capable both, of taking clamping loads and that ofensuring fluid-tightness.

For this purpose, the existing flat gaskets generally comprise a sheetof metal which permits taking loads and has a profile cut out to theshape of the joint plane.

The sheet is also provided with openings corresponding to the passage ofclamping bolts and openings for the passage of the fluids.

On the periphery of the openings corresponding to the passage of fluidsthere is provided a beading of an elastomeric material which provides aseal.

A first important drawback of prior art gaskets is the poor connectionof the elastomeric beading to the metallic sheet.

Indeed, the beading is molded and then secured by bonding solely on theinner surface of the opening. Since, the sheets employed have athickness of a few tenths of a millimeter this surface is very smalland, notwithstanding the fact that the bonding is considerable, themechanical connection remains too weak to resist certain mechanicalstresses, vibrations or shocks.

Moreover such gaskets provide a primary seal solely by means of theelastomeric beading.

There is no secondary seal which would complete this primary seal, sothat any defect in the elastomeric beading results in leakage.

In an attempt to overcome this drawback, prior art gaskets have beenprovided in each of the openings with a projecting annular region whichpermits increasing the bonding area.

In certain cases, improvements involve radially notching the gaskets tostill further increase the bonding area.

Nonetheless, such mechanical connection have been found insufficient formany applications since they provide no secondary seal and do not permitvarying the distribution of the clamping loads.

Some gaskets of the prior art propose a stack of sheets coated with athin layer of elastomer.

On the periphery of the openings to be sealed, the sheets are deformedso as to provide a boss.

In this case, the primary seal is ensured by the boss and the thin layerof elastomer while the secondary seal is ensured by the layer ofelastomer spread over the joint plane.

For gaskets of this kind, the drawback concerns the elastomer, since itis selected from the nitriles family and thickness limited to be a fewtenths of a millimeter and since a material is liable to crack atgreater thicknesses.

Such a gasket thus only has a limited capacity to receive imprints sincethe elastomer does not have a good creep quality.

Consequently, the joint planes must have a very carefully preparedsurface state, which correspondingly increases the cost and samplexityof manufacture.

There is also known from FR-A-1 333 891 a gasket which comprises ametallic core covered with a sealing material and which comprises extrathicknesses in the region of the openings to be sealed. This gasket hasno means adapted to take loads well.

SUMMARY OF THE INVENTION

The present invention proposes a flat gasket, in particular for aninternal combustion engine, comprising at least one metallic sheetforming a reinforcement cut out to the profile of the joint plane andelements of elastomer, in particular of the beading type, deposited andbonded on this sheet in the region of the openings to be sealed,comprises a sanitary packing of elastomer deposited on a part of thesurface of the sheet while forming localized extra thicknesses forsealing in the region of the openings to be sealed with at least onesheet provided with distributed resilient bearing elements on at leastone of the faces of the sheet.

According to another characteristic of the invention, the distributedresilient bearing elements comprise resilient deformations provided inthe sheet or sheets which project from each side of the sheet or each ofthe sheets.

Further, the resilient deformations provided in the sheet or sheets aresymmetrical relative to the median plane of the sheet or each of thesheets.

According to a particular characteristic of the invention, thereinforcement comprises a stack of superposed sheets, one of the sheetsbeing a smooth sheet devoid of a resilient bearing element andperforming the function of a spacer member.

According to a variant of the invention, at least one of the sheets ofthe reinforcement comprises a localized aperture for reducing thestiffness of the gasket in the region of this cut-out part.

The sheets of the reinforcement have variable thicknesses and arepreviously work hardened, provided with lamellar portions and calibratedso as to obtain S-shaped deformations.

According to a particular characteristic of the invention, the packingcomprises impressions on at least one of its two faces so as to improvethe capacity to receive imprints on the joint planes of the parts incontact.

In a preferred embodiment of the invention, the elastomer has a lowdynamic viscosity, being more particularly selected from silicones so asto permit filling the various interstices.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in accordance with a particularembodiment with reference to the accompanying drawings, in which:

FIG. 1, is a partly sectional view of a sheet provided with lamellarportions for manufacturing a flat gasket according to the invention;

FIG. 2, is a partly sectional view of a flat gasket according to theinvention;

FIG. 3, is a partly sectional view of a flat gasket of the multi-sheettype according to the invention; and

FIG. 4, is a schematic sectional view of a flat gasket according to theinvention with the openings for the passage of screws.

FIG. 5 is a schematic sectional view of a flat gasket according to theinvention, comprising two sheets of different thicknesses.

DETAILED DESCRIPTION

In FIG. 1, the reinforcement 10 comprises a metallic sheet 12 which isprovided with lamellar portions 14 each comprising two tongues 16separated by a gap 18. The tongues have a rectangular shape as viewedfrom above, only one of the sides remaining connected to the sheet.

They are produced by cutting, followed by bending and calibration. Inthis way, the S-shaped profile shown in FIG. 1 is obtained.

Each of the tongues of each lamellar portion is in fact a spring in itsown right.

The sheet constructed in this way therefore comprises distributedresilient bearing elements which constitute as many return springs.

The lamellar portions project from each side of the sheet and aresymmetrical with respect to the median plane of the sheet.

In FIG. 1, the lamellar portions 20 and 22 shown in full lines arelamellar portions which are located behind the first row. These lamellarportions are in fact arranged in a staggered manner.

If e is the initial thickness of the sheet, this thickness becomes afree thickness E subsequent to the provision of the lamellar portions.

Shown in FIG. 2 is the gasket proper 24 which is embedded in a matrix 26of elastomer. The gasket is mounted on a part 28 and seals the opening30.

The matrix 26 of elastomer is extended in the region of the end 32 ofthe sheet by a beading 34 having an extra thickness.

The matrix and the beading are unitary with no discontinuity.

In the known manner, grooves 36 are provided in the beading.

The elastomer employed is preferably selected from the silicones or atleast from elastomers having a low dynamic viscosity so that, when it isplaced in position and subsequent to creep, the elastomer comes to fillall the interstices.

In FIG. 3, gasket 24 comprises two superposed metallic sheets 10. Theassembly is embedded in a matrix 26 of elastomer as in the embodiment ofFIG. 1.

In FIG. 4, the gasket comprises two schematically represented superposedmetallic sheets, and an opening 40 for the passage of a belt.

The elastomer may include impressions on its surface so as to improveits capacity to receive imprints. In this case, the surface state of thejoint planes requires less machining.

Further, the flat gasket constructed according to the invention from amulti-sheet reinforcement results in a good distribution of the forcesthroughout the area of the gasket.

Not only is the distribution good, but it is possible to vary it locallyso as to take into account certain regions subjected to higherpressures. For this purpose, it is sufficient to eliminate a part of oneof the sheets making up the reinforcement in the region where it isdesired to reduce the pressure.

The flat gasket according to the invention has many advantages.

First of all, the mechanical resistance of the connection of thebeadings to the reinforcement is excellent bearing in mind the fact thatthe beadings are unitary with the elastomeric matrix in that they aremolded in one piece therewith.

Further, the flat gasket according to the invention provides a doubleseal with a maximum leakage path. Indeed, in addition to the sealobtained on the periphery of each opening with the beadings, there is asecondary seal constituted by the layer of elastomer which covers theentire area of the gasket, and, owing to the nature of the material, theseal in the heart of the gasket is excellent.

Such a gasket also resists heat very well, and this allows applicationsfor fluids of high temperature such as those of the oil circuits ininternal combustion engines.

Another advantage of this gasket is that it permits an easy adaptationowing to the possibility of modifying its height. To obtain differentheights, it is sufficient to insert between the metallic sheets providedwith lamellar portions smooth metallic sheets which perform the functionof spacer members. As these sheets may be selected with small variationsin thickness, the increments in the increase in height are small, whencea good adaptability (see FIG. 5).

In certain applications, the gaskets of different thicknesses aredistinguished by their colors, since the elastomer is mixed withcoloring agents in accordance with a previously-determined color code.

The double seal is particularly advantageous for use in drainage plugs,where very precise centering of the gasket on the plug can be ensured bymeans of one of the sheets of the reinforcement.

We claim:
 1. In an assembly comprising a first planar part, a secondplanar part and clamping means applying clamping loads for tighteningone of said planar parts against the other, a flat gasket intercalatedbetween said planar parts, said gasket comprising a reinforcementincluding at least one metallic sheet combined with a packingconstituted by elastomer, said at least one metallic sheet havingpassage openings to be sealed, said packing comprising portions havingan extra thickness and surrounding said passage openings, wherein atleast one face of said at least one metallic sheet is provided withdistributed resilient load bearing elements extending from said at leastone face towards one of said planar parts and terminating in a freebranch which is substantially parallel to said one of said planar parts,and wherein said resilient load bearing elements are adapted to takesaid clamping loads and, upon variation of said clamping loads, to biassaid packing toward said one of said planar parts.
 2. The gasketaccording to claim 1, wherein said load bearing elements compriseresilient deformations provided in said metallic sheet and projectingfrom both sides of said metallic sheet.
 3. The gasket according to claim2, wherein said resilient deformations project symmetrically relative toa median plane of said metallic sheet.
 4. The gasket according to claim1, wherein said reinforcement comprises a stack of superposed sheets, atleast one of said sheets of said stack being provided with saiddistributed resilient bearing elements and at least one other of saidsheets of said stack being a smooth sheet devoid of a resilient loadbearing element and acting as a spacer member.
 5. The gasket accordingto claim 4, wherein said stack of sheets comprises at least two smoothsheets having different thicknesses.
 6. The gasket according to claim 1,wherein said metallic sheet of said reinforcement comprises a localizedaperture for reducing a stiffness of said gasket at a location of saidaperture.
 7. The gasket according to claim 1, wherein said metallicsheet is a previously work-hardened sheet, provided with lamellarportions and calibrated so as to obtain deformations having an S-shapedcross-section.
 8. The gasket according to claim 1, wherein at least oneface of said packing comprises impressions adapted to receive imprintsof said joint planes of said parts in contact with said gasket.
 9. Thegasket according to claim 1, wherein said elastomer is a siliconeadapted to fill interstices provided in said metallic sheet.